Boosting peripheral BDNF rescues impaired in vivo axonal transport in CMT2D mice

Abstract

Gain-of-function mutations in the housekeeping gene GARS1, which lead to the expression of toxic versions of glycyl-tRNA synthetase (GlyRS), cause the selective motor and sensory pathology characterising Charcot-Marie-Tooth disease (CMT). Aberrant interactions between GlyRS mutants and different proteins, including neurotrophin receptor TrkB, underlie CMT type 2D (CMT2D); however, our pathomechanistic understanding of this untreatable peripheral neuropathy remains incomplete. Through intravital imaging of the sciatic nerve, we show that CMT2D mice display early and persistent disturbances in axonal transport of neurotrophin-containing signalling endosomes in vivo. We discovered that BDNF-TrkB impairments correlate with transport disruption and overall CMT2D neuropathology, and that inhibition of this pathway at the nerve-muscle interface perturbs endosome transport in wildtype axons. Accordingly, supplementation of muscles with BDNF, but not other neurotrophins, completely restores physiological axonal transport in neuropathic mice. Together, these findings suggest that selectively targeting muscles with BDNF-boosting therapies could represent a viable therapeutic strategy for CMT2D.

Boosting BDNF in muscle rescues impaired axonal transport in a mouse model of DI-CMTC peripheral neuropathy

“…Disturbances in axonal transport have been identified in models of many different forms of both genetic and acquired peripheral neuropathy (74)(75)(76), including cellular and in vivo models of CMT2D (27,42,77,78); however, whether these deficits are a primary cause of disease or simply a secondary consequence of neuropathology remains an open question. While we have not determined whether impaired endosome trafficking is a driver of neuropathy in Yars E196K mice, we do provide the first evidence for its dysfunction in DI-CMTC and only the second study in which axonal transport has been identified as being impaired in mammalian peripheral neuropathy in vivo.…”

“…Sciatic nerves and tibialis anterior muscles were dissected from PBS-perfused and non-perfused mice. Proteins were extracted from NSC-34 cells and tissues, and evaluated by western blotting as detailed previously (42). Primary and secondary antibodies used for western blotting are detailed in Table S2 and Table S3, respectively.…”

“…Non-normally distributed data were analysed using a Wilcoxon matched-pairs signed rank test or Kruskal-Wallis test followed by Dunn's multiple comparisons test. Sample sizes, which were pre-determined using power calculations and previous experience (26,42,47,48,54,56,57), are reported in figure legends and represent biological replicates (i.e., individual animals). Means ± SEM are plotted for all graphs.…”

“…To do this, we transfected NSC-34 cells with constructs encoding V5-tagged human TyrRS WT , TyrRS E196K or GlyRS ∆ETAQ , with the latter included as a positive control (42). Cells were subsequently lysed and co-immunoprecipitation experiments performed with the ECD of Fc-tagged TrkB (Figure 1A).…”

“…In this study, we therefore set out with two main aims: 1) to determine whether the E196K mutation in YARS1 enables a similar pathological association with the extracellular domain (ECD) of TrkB as that found in CMT2D-linked GARS1 mutants (26,42); and 2) to provide a detailed temporal characterisation of neuromuscular phenotypes in Yars E196K/+ and Yars E196K/E196K mice in order to evaluate the neuropathological similarities between ARS-linked neuropathies in a mammalian setting.…”